IIRC the KE schedule includes an A380 nonstop year round that departs JFK around midnight and arrives at ICN very early in the morning, so that you can connect elsewhere on their first morning bank of departures. This could work very well for business travel.

There might be a KE flight from BOS to ICN too.

Obviously there are other possibilities for using DL or KE to ICN for the onward connections on KE. DL operated flights have either C+ (essentially the same as Y+ on UA, meaning coach seats with more legroom etc.) or new Premium Economy sections (for instance on the A350 DTW-ICN and new A350 MSP-ICN and vv routes). You can also connect through LAX, ATL, SEA, etc. The price difference compared to regular coach might not be unreasonable.

Finally, remember that you can avoid the DL MQD requirement ($6,000 spend on DL fares and fees for Gold, including partner flights where the calculation often is in your favor) by spending $25,000 per year on almost anything (not including annual fees, cash advances, interest charges, etc.) on your DL AmEx Plat or Reserve credit card(s). You also earn an extra redeemable mile or two per dollar for DL tickets charged to these DL affiliated cards. The Reserve card (high annual fee) includes DL lounge access when flying DL, including on cheap domestic coach tickets or award tickets.

For CAN, there might be a CZ nonstop from JFK; they surely fly from LAX (and probably YVR/SEA/SFO too). MU would offer service, at least from the west coast, through Shanghai and/or Beijing, which isn't so convenient and puts you in the path of notorious mainland China ATC delays for military exercises, etc.